What is the filter efficiency percentage of a HEPA filter?

HEPA filters, or High-Efficiency Particulate Air filters, are designed to trap a high percentage of very small particles, making them essential in environments where air quality is a priority, such as in medical facilities and laboratories. The standard efficiency of a true HEPA filter requires it to capture at least 99.97% of particles that are 0.3 micrometers in diameter. This specification is based on the most penetrating particle size (MPPS), which indicates that particles at this size are the most difficult to filter out.

The high filtration efficiency is due to the structure of the filter, which contains a dense mat of fibers that capture particles through various mechanisms, including interception, inertial impaction, and diffusion. The value of 99.97% reflects the ability of HEPA filters to effectively remove almost all airborne particulates, which is crucial in maintaining safe and clean air environments.

While there are filters with different efficiency ratings — for example, filters that capture 95% or 98.5% of particles — these do not meet the strict HEPA standards. Hence, they cannot provide the same level of protection and are not classified as HEPA filters. The designation of a filter as a true HE